Washed Cotton in The 1978 OSHA Cotton Dust Standard

Current Intelligence Bulletin 56

Additional Studies

Additional studies were subsequently conducted under the auspices of a tripartite (government/ industry/union) Task Force on Washed Cotton Evaluation (now the Task Force for Byssinosis Prevention), which comprised the following member organizations: Agricultural Research Service (formerly the Science and Education Administration) (U.S. Department of Agriculture); National Institute for Occupational Safety and Health (U.S. Department of Health and Human Services); National Cotton Council of America; Cotton Incorporated; American Textile Manufacturers Institute; and Amalgamated Clothing and Textile Workers Union.

These extensive and carefully controlled human exposure studies demonstrated that mild washing (essentially water rinsing) of cotton on a continuous batt or rayon rinse system has two major effects relevant to occupational respiratory disease prevention among cotton textile workers. First, mild washing physically removes dust from the cotton, generally reducing subsequent generation of respirable dust by about 50% (range, 35% to 67%). Second, mild washing markedly reduces the acute airway toxicity of residual dust, as measured by acute ventilatory responses of experimentally exposed human subjects. Both beneficial effects were shown to vary somewhat depending on specific washing methods used and on the initial potency of the cotton washed. Details have been published elsewhere [Wakelyn et al. 1986].

In contrast to mildly washed cotton from continuous batt and rayon rinse systems, mildly washed cotton from a batch kier washing system (though clearly much less potent than unwashed cotton dust) was found in some cases to retain significant acute airway activity in the human exposure studies, as measured by acute ventilatory responses [Castellan 1986]. The variable results observed were attributed to channeling of wash and rinse solutions through the cotton, which prevented thorough removal of dust and soluble material from the cotton fibers. Channeling was caused by hand loading directly from the bale without mechanical opening, cleaning, or prewetting.

1985 Exemptions for Washed Cotton

In 1985,on the basis of a review of the existing data, comments, and Task Force recommendations [OSHA Docket H-052], OSHA substantially revised the washed cotton provision in the cotton dust standard. In clarifying the previously ambiguous washed cotton exemption, the revised standard provides a complete exemption only for "medical grade (USP) cotton, cotton that has been scoured, bleached and dyed, and mercerized yarn" [OSHA 1985]. Importantly, the 1985 revision adds partial exemptions for mildly washed cotton (as described in the following paragraphs); but consistent with Task Force recommendations, it provides no exemptions for batch kier washed cotton [50 Fed. Reg. 51120 (1985)].

Exemption from all requirements of the standard except for medical surveillance and medical recordkeeping is provided for higher grade cotton (low middling light spotted, or better—i.e., color grade code 52 or better and leaf grade code 5 or better according to the current classification system [USDA 1993a]) that is washed: (1) on a continuous batt system or rayon rinse system, (2) with water, (3) at a temperature of no less than 60°C, (4) with a water-to-fiber ratio of no less than 40:1, and (5) with bacterial levels in the wash water controlled to limit bacterial contamination of the cotton.

Lower grade cotton (i.e., below color grade code 52 or below leaf grade code 5 by the current classification system [USDA 1993a]) that is washed as specified in the preceding paragraph for higher grade washed cotton and is also bleached is exempted from all requirements of the standard except for medical surveillance, medical record- keeping, and a 500-µg/m3 PEL for airborne dust measured by the vertical elutriator sampler. With respect to washed cotton of mixed grades, the 1985 revised standard specifies that the requirements for the grade with the most stringent requirements would apply.

Limitations of the 1985 Partial Exemptions for Mildly Washed Cotton

The availability of continuous batt washing systems (including rayon rinse systems) for washing cotton is extremely limited. The continuous batt system used in the Task Force evaluations had a production capacity of only 500 lb/hr and is unavailable for commercial washing of cotton. The rayon rinse system has a much lower production rate for washing cotton, and the few rayon rinse systems available in the United States are fully utilized in rayon production. In contrast, production capacity on modern batch kier systems is much higher, and essentially all cotton washing for medical uses (e.g., cotton balls, surgical sponges, etc.) and essentially all cotton dyeing for textile uses (e.g., stock dyeing for denim products, etc.) utilizes batch kier processes.

OSHA's Director of Policy anticipated the limitations of the 1985 revised standard in stating that "OSHA hopes to receive additional information as to acceptable cotton washing methods and alternative ways of predicting human respiratory response to cotton dust exposure" [Goldin 1984]. This, together with the projected availability of batch kier systems (in contrast to continuous batt or rayon rinse systems) for washing cotton, and along with improved technology for modern batch kier systems already in use for medical grade washing and stock dyeing of cotton, led to further evaluations of batch kier systems as a means of pretreating cotton to reduce toxicity.